Heart Failure (HF) is a chronic condition that affects over 5 million Americans and, according to the American Heart Association, HF accounts for more hospitalization among elderly people than any other condition. HF is not a condition in which the heart abruptly stops beating. Instead, HF refers to a dysfunction in the pumping action of the heart due to the heart's inability to contract or relax properly. It is generally experienced by patients who have suffered a heart attack or whose hearts have been damaged by other conditions which have disrupted the heart's natural electrical conduction system.
Patients with heart failure generally experience breathlessness, fatigue and fluid build-up in the arms and legs. This is caused by the heart's inability to pump enough blood to meet the body's demands. The heart can become enlarged as it attempts to compensate for the lack of pumping ability, which only worsens the condition. Typically, it is the lower chambers of the heart (ventricles) that do not beat efficiently (e.g., ventricular dyssynchrony) resulting in an increasingly ineffective heart. However, with HF, the upper chambers (atria) can also become enlarged or experience disruption in electrical conduction (e.g., atrial dyssynchrony).
The right ventricle is responsible for pumping blood to the lungs while the left ventricle is responsible for pumping blood to the rest of the body. The right atrium fills the right ventricle with deoxygenated blood while the left atrium fills the left ventricle with oxygenated blood. In a normal heart, the atria contract to fill the ventricles and then the ventricles contract in a synchronous manner to pump blood through the lungs or the body. Abnormal activation of any of the heart's four chambers reduces pumping efficiency. For example, abnormal ventricular activation can decrease ventricular filling, cause abnormal ventricular wall motion and cause mitral valve regurgitation (MR). Standard pharmacologic therapy cannot adequately resolve conduction and activation abnormalities such as left bundle branch block (LBBB) or a lengthy interventricular conduction delay (IVCD) that contribute to ventricular dyssynchrony.
Cardiac Resynchronization Therapy (CRT) provides an electrical solution to the symptoms and other difficulties brought on by HF. In many CRT systems, electrical impulses can be delivered to the tissue in the heart's two lower chambers (and typically one upper chamber). This is called biventricular pacing, and it causes the ventricles to beat in a more synchronized manner. Biventricular pacing improves the efficiency of each contraction of the heart and the amount of blood pumped to the body. This helps to lessen the symptoms of heart failure and, in many cases, helps to stop the progression of the disease. For patients fitted with CRT systems, clinical studies show improved quality of life (QOL), NYHA functional class, exercised tolerance, left ventricular reverse remodeling, morbidity and mortality.
For proper operation, values for a handful of CRT system parameters must be determined. In general, a clinician determines such values using information acquired from an echocardiography examination of a patient. Once the parameter values have been determined, the clinician can then program the patient's implantable CRT device. Some newer CRT systems include algorithms that can determine CRT parameter values based on cardiac electrograms measured by a patient's implantable CRT device. For example, the QUICKOPT™ algorithm (St. Jude Medical Corporation, Sylmar, Calif.) can determine AV, PV, and VV intervals in about a minute using intracardiac electrogram (IEGM) information. Noting that clinical evidence demonstrates that timing cycle optimization improves outcomes to CRT therapy and that optimal delays change over time, the QUICKOPT™ algorithm allows for efficient, frequent optimization. Further, QUICKOPT™ optimization is clinically proven to correlate with echo based techniques.
As described herein, various exemplary techniques acquire information (e.g., measurements and/or parameter values) and analyze such information to monitor cardiac condition and/or CRT performance. In turn, knowledge of cardiac condition and/or CRT performance can be used to optimize patient therapy.